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Show 1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 449 I am disposed to regard this ossicle and its fellow as the representatives of the vomers, which, if this interpretation be correct, remain exceptionally distinct from one another, but unite with the palatines. The antero-internal angle of the body of the palatine bone sends forwards a slender process, which forms the inner boundary of the posterior half of the palatine foramen. The maxillo-palatines are broad plates, which appear to terminate by rounded internal edges close to and above the external margins ot the palatines. But a tough membrane extends inwards from the free edge of each maxillo-palatine and meets with a delicate longitudinal ossification of the septum (a, fig. 30). Opposite the anterior termination of the external nasal aperture this ossification is connected with a transverse bar of bone, which stretches from one praemaxilla to the other, and shuts off the cavity enclosed by the praemaxillae from the nasal chambers. The latter are greatly complicated by the development of twisted "turbinal" plates in connexion with the nasal and premaxillary bones and the ethmoid. A prolonged and careful study of fresh specimens will be necessary before the arrangement of the parts in Picus can be thoroughly understood. In the meanwhile it is clear that, in this genus, the palate differs very widely from that observed in any of the preceding " cuculiform " genera. In Picus major the palatine bones have the same structure and arrangement as in P. viridis, except that their posterior ends are transversely truncated and the postero-external angles are even a little produced. The maxillo-palatines are much smaller than in the preceding species, and their inner rounded edges do not nearly reach the level of the outer edges of the palatines. Picus canus resembles the preceding; but the postero-external angles of the palatines are rather better marked, and the maxillo-palatines a little larger. Picus medius presents no difference of importance, except that the inner laminae of the palatines, obsolete in the other genera, are a little better marked, especially behind. In Picus minor distinct maxillo-palatines can hardly be said to be present, the maxillary presenting only a slight dilatation at the point where they should exist. Minute points of bone projecting from the inner edges of the palatines alone indicate the position of the process (c) in Picus viridis and of the prolongation of the antero-internal angle of the body of the palatine. The " oval foramen " consequently is indicated only by a slight excavation of the inner margin of the palatine. This species of Picus prepares one in some degree for the structure observed in Yunx (fig. 31). Here the ascending processes of the palatine bones are produced forwards into long and slender processes, slightly swollen at their anterior free ends, which may represent anchylosed vomers. The inner edges of the short and broad bodies of the palatine bones approach so nearly as only to leave a cleft for the posterior nares. The antero-internal angles are acute, but not greatly prolonged. The anterior processes of the palatines are very P R O C ZOOL. Soc-1867, No. XXIX. |
